Abstract:
In active catheter tracking, a microcoil directly connected to the MRI system and positioned at the distal end of the catheter is employed for localization. The peaks in the frequency spectrum of the acquired MR signal correspond to catheter's physical location. The major problem with active techniques is the RF heating due to long conducting wires. Fully optical systems that replace the conducting wires with inherently RF-safe optical bers are proposed. In these systems, the SNR su ers from the electro-optical signal conversion distally (and opto-electrical conversion proximally) at this high frequency. Amplifying and frequency down-converting the MR signal at the catheter tip could minimize signal losses. Ampli cation could be achieved with an LNA placed next to the microcoil. To provide the reference signal to the mixer for frequency down-conversion of the ampli ed MR signal, an outside generator or onchip oscillator could be used. Both methods have their disadvantages like increased complexity at the distal end due to additional cable and frequency drift over time due to temperature or bias voltage variations. In this work, the reference signal for frequency down-conversion is provided from the MRI scanner's own transmitter! It is a very reliable source of signal since no frequency drift for the transmitter is expected over a speci c imaging sequence interval. The frequency of the reference signal is de ned as an o set with respect to the center frequency of the scanner, making this technique immune to main eld drifts. Following down-conversion, the electrical signal is converted into optical signal for MRsafe transmission. This is also critical to protect the circuitry of the distal unit and receiver from currents that would be induced on the outer surface of the cable.|Keywords : interventional MRI, device localization, catheter tracking, optoelectronics.
